The effect of mycorrhizal inoculation on the rhizosphere properties of trifoliate orange (Poncirus trifoliata L. Raf.)

Key rhizosphere properties influenced by microorganism-mediated processes need to be identified for better understanding of their possible role in improving crop performance. This study monitored the changes in concentration of Bradford-reactive soil protein (BRSP), soil organic carbon (SOC) content, hyphal length, aggregate stability [fractal dimension (D), geometric mean diameter (GMD), and mean weight diameter (MWD)] and distribution of water-stable aggregate (WSA) in rhizosphere of trifoliate orange (Poncirus trifoliata L. Raf.) infected by five arbuscular mycorrhizal fungal species (Diversispora spurca, Glomus intraradices, Glomus mosseae, Glomus versiforme, and Paraglomus occultum). After four months of mycorrhizal inoculation, all the mycorrhizal plants showed higher shoot and root biomass but the increase was a function of the tested fungal species. The induced changes in rhizosphere properties were of much higher magnitude in mycorrhizal treatment than in non-mycorrhizal treatment. Mycorrhizal inoculation induced significant increases in the percentage of WSA at 1.00-2.00 mm size, fraction 1 of BRSP, SOC, and hyphal density, collectively aiding in improving the indices of soil aggregate stability, like GMD and MWD. Higher MWD and GMD conferred better soil structure in mycorrhizosphere of trifoliate orange. Correlation analysis further revealed that fraction 1 of BRSP as a new and more active glomalin may take part in stabilizing WSA but fraction 2 of BRSP as an older and more stable glomalin may contribute SOC pools. Our results suggest that mycorrhizal-mediated better soil aggregate stability might mainly be due to soil hyphal length, integrated with SOC and fraction 1 of BRSP.